This invention is related to semiconductor laser devices and, more particularly to semiconductor laser devices with replaceable laser diode bars.
A number of lasers, such as slab and rod lasers, are designed to produce output pulses having a high average output power, such as 1,000 W–10,000 W, operating either continuously or in a repetitively pulsed mode. High levels of output power are required in a number of applications including laser radar, mine detection, welding, material processing, surface coating, isotope separation and x-ray lithography, among others. In order to obtain such high power levels, a primary laser, such as a slab or a rod laser, can be pumped by a laser pump source, such as an array of semiconductor laser diodes. The laser pump source must also operate at relatively high power levels and either at relatively high pulse repetition rates or continuously in order to generate the necessary power to excite the primary laser.
Semiconductor lasers that pump a primary laser are typically made of multiple linear arrays of laser diodes, also known as linear laser diode bars. The linear laser diode bars are then arranged in a two-dimensional laser diode array. To form the two-dimensional laser diode array, the linear laser diode bars are typically soldered on microchannel heat sinks, which are subsequently stacked. The two-dimensional laser diode array is capable of generating high intensity light for pumping the primary laser.
Although the soldered two-dimensional laser diode array design is suitable for laser applications, it creates significant difficulty when individual linear laser diode bars must be replaced. The linear laser diode bars occasionally fail for a variety of reasons, such as facet erosion (also called “spewing”), solder bonding failure, overheating, dark line defect growth, and gradual degradation, and must be replaced. Because the linear laser diode bars are soldered on heat sinks, however, the bars cannot be easily removed and reinserted. Instead, the entire two-dimensional laser diode array must either be scrapped or, if a repair is to be attempted, the entire array typically must be disassembled by breaking the solder joints, if possible, replacing the failed bar, and reassembling the array by resoldering the new laser diode bar into position, then resoldering the array together. Because of the difficulty involved in breaking the solder joints and resoldering the array, the replacement of conventional linear laser diode bars cannot be performed by a typical user of a semiconductor laser device. In fact, the replacement process typically cannot even occur at or near the location at which the semiconductor laser device is deployed. Instead, the semiconductor laser device should be returned to its manufacturer or a maintenance depot for repair, which can take weeks. Thus, the semiconductor laser device is inoperable and unavailable during the time it is being repaired and during the time it is in transit to and from the manufacturer.
Replacing a linear laser diode bar in a two-dimensional laser diode array, therefore, can be costly to users of the semiconductor laser devices who must be without the device for weeks while it is being repaired. In addition, it is costly and labor-intensive for the manufacturers of such semiconductor laser devices or for other maintenance personnel to make the repairs necessary when a linear laser diode bar must be replaced. As such, there is a need in the industry to provide a two-dimensional laser diode array for use in semiconductor laser devices, in which the individual linear laser diode bars may be easily and immediately replaced without having to disassemble the entire array and without a significant investment of time and/or money.
Thermal heat dissipation is another concern for semiconductor lasers. In this regard, in generating pulses having a relatively high average output power and a relatively high repetition rate, the laser pump source generates a significant amount of heat, which elevates the temperature of the laser pump source in the absence of external cooling. For example, the heat generated by a laser can be approximated by the difference between the power input to the laser and the output power received from the laser. Typically, the heat generated by a conventional laser pump source is approximately 45%–60% of the input power, with the overall efficiency of a solid state laser comprised of a laser pump source and a downstream laser system being about 10%–20%.
Lasers, such as semiconductor laser diode arrays, however, typically have a maximum operating temperature above which the operation of the laser can be unreliable. In addition, operation of a laser, such as a semiconductor laser diode array, at an elevated temperature generally reduces the effective lifetime of the laser even though such temperatures may be below the maximum operating temperature. For example, operation of a semiconductor laser diode array at an elevated temperature can damage the emitting facet of the laser diode array, thereby impairing its performance.
One type of semiconductor laser diode array that provides suitable cooling during laser operation, while also being economical to produce compared to other semiconductor laser diode arrays, is the immersion cooled array. An immersion cooled array is made from linear laser diode bars mounted on microchannel coolers. The simple linear laser diode bars are capable of continuous wave (CW) or high duty factor operation by clamping the bars to liquid cooled heat sinks, and immersing the entire two-dimensional laser diode array in a flowing dielectric coolant. Details of the immersion cooled array are included in U.S. Pat. No. 5,495,490, which is incorporated herein by reference.
Because of the time and expense involved in replacing individual linear laser diode bars in conventional laser diode arrays, it would be advantageous to be able to quickly and easily replace individual linear laser diode bars in laser diode arrays. In particular, there is a need in the industry to utilize two-dimensional laser diode arrays, such as immersion cooled arrays, in semiconductor laser diode devices, in which the arrays include individual linear laser diode bars that are easily and immediately replaceable without a significant investment of time and/or money. Furthermore, due to the efficient and economical nature of the immersion cooled array, it would be desirable to be able to utilize such an immersion cooled two-dimensional laser diode array made from removable linear laser diode bars in a variety of applications.